PbI2‐DMSO Assisted In Situ Growth of Perovskite Wafers for Sensitive Direct X‐Ray Detection

Abstract Although perovskite wafers with a scalable size and thickness are suitable for direct X‐ray detection, polycrystalline perovskite wafers have drawbacks such as the high defect density, defective grain boundaries, and low crystallinity. Herein, PbI2‐DMSO powders are introduced into the MAPbI3 wafer to facilitate crystal growth. The PbI2 powders absorb a certain amount of DMSO to form the PbI2‐DMSO powders and PbI2‐DMSO is converted back into PbI2 under heating while releasing DMSO vapor. During isostatic pressing of the MAPbI3 wafer with the PbI2‐DMSO solid additive, the released DMSO vapor facilitates in situ growth in the MAPbI3 wafer with enhanced crystallinity and reduced defect density. A dense and compact MAPbI3 wafer with a high mobility‐lifetime (µτ) product of 8.70 × 10−4 cm2 V−1 is produced. The MAPbI3‐based direct X‐ray detector fabricated for demonstration shows a high sensitivity of 1.58 × 104 µC Gyair−1 cm−2 and a low detection limit of 410 nGyair s−1.

Synthesis of PbI 2 -DMSO compound. 4.61 g of the yellow PbI 2 powder were dissolved in 10 mL of DMSO to form a PbI 2 solution. The solution was stirred until it became clear. 1 ml of lead iodide dimethyl sulfoxide was added to 50 ml of acetone to form white flocs. The precipitate was obtained by filtration and dried in a vacuum at 40 ℃ to obtain pure white powder.

Synthesis of MAPbI 3 powder.
The MAPbI 3 microcrystals were synthesized by the anti-solvent assisted precipitation method. CH 3 NH 3 I (0.6358g, 4 mmol) and PbI 2 (1.8440g, 4 mmol) crystals with a ratio of 1:1 were dissolved in 5 ml DMF to form a 4 mM solution. 1 ml of the mixture was injected into 15 ml of chloroform to form MAPbI 3 nanocrystalline precipitates within a few seconds. After standing for a period of time, the microspheres were washed twice with chloroform in a centrifuge and dried in a vacuum oven at 50 ℃ overnight.
Preparation of the MAPbI 3 wafer. 0.41 mg of MAI, 1.40 mg of PbI 2 -DMSO, and 180 mg of MAPbI 3 , were weighed and mixed. The mixed powders were then filled to a pie shape (dimensions of 1 cm × 1 cm) and pressed to 10 MPa at 100℃ for 90 min. The heat-assisted pressing process produced the black perovskite wafer with a mirror surface. Thereafter, the wafer was annealed at 100 ℃ for 30 min in a glovebox to evaporate residual DMSO and further crystallized. Scientific, Nicolet iS50) using the KBr pellet method. Powder X-ray diffraction (XRD) was performed on the Rigaku Smartlab 3kW X-ray diffractometer with Cu K α radiation ( = 1.54056 Å, 40 kV, 30 mA, 10° min −1 from 10 to 60°). The UV-vis absorption spectra were obtained on a UV-vis spectrophotometer (UV-1800, Shimadzu). Raman scattering was carried out on the Horiba Jobin Yvon LabRam HR-VIS high-resolution confocal Raman microscope equipped with a 633 nm laser.
The PL and TRPL properties were determined by fluorescent spectrophotometry (Hitachi F-4600 and Edinburgh FLS-1000) using an excitation wavelength of 365 nm.
The PL spectra were automatically recorded every 100 ms during the PL measurement.
The time-resolved photoluminescence (TRPL) spectra were recorded by a time-correlated single-photon counting spectrometer (Horiba, FluoroMax-4) with an excitation source of 365 nm laser.
Device characterization. The X-ray detection properties of the detector were evaluated using an X-ray generation system for medical imaging (Varex, G242, 18932-M8, USA). The accelerating voltage was 50 kV and the currents were varied from 10 to 200 uA. The dose rate of the X-rays was strictly calibrated using an X2 CT dosimeter (Unfors Raysafe, Sweden). During the measurement, the environment was kept dark and the external electrical bias and current were recorded by the PDA FS380 semiconductor analyzer. The X-ray imaging capability of the detector was demonstrated by moving the investigated object between the detector (3.14 mm 2 ) and X-ray beam (1.62 mGy air s -1 ) using a self-assembled x-y scanning system. The home-made x-y scanning system consisted of a motorized linear displacement stage (Newport, M-IMS400CC. A motorized linear displacement stage combined with a motion controller (Newport, M-IMS400CC) was used to control the scanning along the x and y axes.